1. Field of the Invention
The present invention relates to the manufacturing of decorative surfaces using inkjet technology.
2. Description of the Related Art
Gravure, offset and flexography are being increasingly replaced for different applications by industrial inkjet printing systems, which have now proven their flexibility in use, such as variable data printing making short production runs and personalized products possible, and their enhanced reliability, allowing incorporation into production lines.
Inkjet technology has also caught the attention of manufacturers of decorative surfaces, such as laminate floor. In the current production process for manufacturing decorative panels as shown by FIG. 1, a paper manufacturer (11) supplies a paper roll (12) to a decor printer (13) who uses gravure printing (14) in order to deliver a decor paper roll (16) to a warehouse (17) of a floor laminate manufacturer (20). Some decor printers (13) are now investigating inkjet printing (15) instead of gravure printing. Rotogravure printing on the porous decor paper generally uses ink having a viscosity at 25° C. of 1 to 2 Pa·s. The viscosity of inkjet inks is much lower, often about 1 to 15 mPa·s at 25° C., which makes it necessary to use a more expensive paper having a special ink-receiving layer in order to obtain a good image quality. The floor laminate manufacturer (20) stores the decor paper rolls (16) having different decorative patterns in his warehouse (17). Depending on the market demand, the floor laminate manufacturer (20) then selects the decor rolls (16) with the desired decorative pattern from his warehouse (17). The selected decor rolls (16) are then impregnated (18) and cut to size (19) for manufacturing ready-to-use floor laminate (21). The warehouse (17) is necessary as a buffer for sudden large market demands of a specific floor laminate because there is a large time delay between ordering and delivering of new decorative paper rolls (16). Often the floor laminate manufacturer (20) also has a second warehouse (not shown) containing resin impregnated printed sheets available for manufacturing ready-to-use floor laminate (21) when manufacturing problems or delays occur in the impregnation line.
An approach to reduce the size of the warehouse and time delays is treated by EP 2431190 A (THEODOR HYMMEN), which discloses in FIG. 1 a method for producing a digitally printed sheet, web or plate-shaped workpiece (20) with wear-resistant surface including the steps of:
A) providing a digital data set to a digital printing device (1);
B) providing a printable workpiece (20) to the printing apparatus (1);
C) digital printing at least an acrylate printing ink (22) on the printable workpiece (20) using the printing apparatus (1) and thereafter supplying a resin mixture (5, 21) to the digitally printed workpiece; and
D) curing the resin mixture (5, 21) by means of a heated press (7). The time delay can be avoided by the floor laminate manufacturer incorporating the manufacturing of decorative paper rolls into its own production process. EP 2431190 A (THEODOR HYMMEN) discloses in FIG. 2 the use of a paper substrate having a special ink receiving layer (23), which in combination with a more expensive acrylate ink only increases the cost of the final product. Furthermore, paragraph [0003] discloses that the use of acrylate ink leads to adhesion problems between the reactive melamine resin mixture and the acrylate ink, requiring specific measures like crosslinking agents that react only above 50° C. or 70° C., making the manufacturing process less robust. Another way to resolve this problem is to replace the melamin resin impregnated protective layer by a less wear resistant acrylate varnish layer.
Hence, there is still a need for improved manufacturing methods of decorative surfaces using inkjet technology and melamine resin as a wear coating.